[hpsdr] My doubts about I/Q beam-forming

[Murray Lang]

Hi Ken,

No I don't, but I'll try to look it up. I've seen an article on (RX) 
beamforming with "SDR" where they directly sample the RF using a separate 
A/D for each line and synchronise the LO clocks. I believe a similar result 
can be achieved by synchronising clocks on multiple QSDs/QSEs. But here the 
phase adjustment is through RF PLLs.

My posting was actually a continuation of an earlier discussion where it 
was proposed that beamforming could be manipulated via I/Q. I wasn't 
comfortable with it at the time, but couldn't explain why beyond a vague 
worry about I/Q frequency response.

Murray - VK6HL

At 08:36 AM 5/09/2006, Ken - N9VV wrote:
>Hi Murray, I am probably way off base here, but there was an article in 
>QEX this past month about what looks like what might be beamforming for 
>microwave freqs using phased arrays and SDR/DSP. Do you have access to a 
>copy of QEX?
>de ken n9vv
>
>
>Murray Lang wrote:
>>***** High Performance Software Defined Radio Discussion List *****
>>My doubts about the ability to do RF beam-forming via I/Q have clarified 
>>somewhat.
>>Beam-forming would seem feasible given that you can modulate a carrier 
>>any way you like with I/Q. However, the *resolution* of that modulation 
>>is limited by the I/Q bandwidth and dynamic range. To accurately and 
>>steadily control the phase of an RF carrier to within a small fraction of 
>>its wavelength would require an I/Q  bandwidth of the same order as the RF.
>>Would it not?
>>Murray - VK6HL
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